Quantitative analysis and comparison of the physical properties of O-alkyl and S-alkyl monoethers of glycerol

A homologous series (C(10), C(12), C(14), C(16), C(18)) of synthetic O-alkyl and S-alkyl ethers of glycerol was analyzed by gas-liquid chromatography (GLC) and thin-layer chromatography (TLC), and examined by IR and n.m.r. spectroscopy; the physical properties of the O-alkyl and S-alkyl ethers were compared. Isopropylidene derivatives of the glycerol ethers and thioethers were quantitatively analyzed by GLC on polar and nonpolar liquid phases. On a medium polar liquid phase (ethylene glycol succinate), mixtures of the O-alkyl and S-alkyl ethers were completely resolved. Isopropylidene derivatives of glycerol ethers and of thioethers could be separated as classes (though not into individual homologues) by TLC. O-hexadecyl and S-hexadecyl ethers of glycerol are easily distinguished by IR and n.m.r. spectroscopy.     

Two-column gas chromatography of trimethylsilyl derivatives of biochemically significant compounds

Gas chromatographic (GC) retention data as methylene unit (MU) values are presented for the trimethylsilyl (TMS) derivatives of 250 biochemically significant compounds on two different GC stationary phases (OV-1 and OV-17). A ΔMU value is calculated for the difference in MU values on the moderately polar OV-17 and the nonpolar OV-1 columns. Some relationships between ΔMU values and structure are discussed; in general highly polar compounds have large ΔMU values and those compounds forming derivatives containing several TMS groups have low ΔMU values. Compounds in the following categories were studied: amino acids; organic acids; aromatic acids, amines, and glycine conjugates; and purines, pyrimidines, and other nitrogen heterocyclic compounds.     

Temperature-dependent molecular motions and phase behavior of cholesteryl ester analogues

The phase behavior and temperature-dependent molecular motions of three cholesteryl ethers (caproyl, myristyl, oleyl) and a cholesteryl carbonate (oleyl) were characterized. The properties of each ether were qualitatively similar to, but quantitatively different from, those of the corresponding cholesteryl ester. For example, cholesteryl oleyl ether exhibited the same phase transitions as cholesteryl oleate, but at much lower temperatures (e.g., the ether isotropic liquid to cholesteric transition is at 29 degrees C). 13C NMR spectra of ethers in the isotropic liquid and liquid crystalline phases were similar to those of the ester analogue. However, near the liquid to liquid crystalline transition, the steroid ring C3 and C6 linewidths, the C3/C6 linewidth ratio, and the steroid ring rotational correlation times tau rx and tau rz calculated from the linewidths were larger for the ether than the ester analogue. The oleyl carbonate had qualitatively different properties from its analogues (e.g., stable vs. metastable cholesteric and smectic phases). Quantitative results (e.g., relatively long tau rx and tau rz in the isotropic liquid phase) for the carbonate were also distinct from those of both the ester and ether analogues. A comparison of analogues in which the polar linkage is the only structural variable yielded insights into the intermolecular interactions which influence phase behavior.     

Gas-liquid chromatography of dialkyl, alkyl acyl, and diacyl ddrivatives of glycerol

Dialkyl, alkyl acyl, and diacyl glycerols were resolved as trimethylsilyl ethers and as acetates by gas-liquid chromatography on a nonpolar stationary phase (OV-1). The two types of derivatives proved suitable for quantitative gas chromatographic analysis.     

Gas chromatographic-mass spectral characteristics of aporphine and tetrahydroprotoberberine alkaloids

The gas chromatographic (GC) and mass spectrometric (MS) properties of the silyl derivatives of aporphine and tetrahydroprotoberberine alkaloids are described. Selected representatives of these chemical classes of pharmacologically active bases were chromatographed on polar (OV-17) and nonpolar (OV-1) columns as their trimethylsilyl derivatives. The aporphines were eluted before the tetrahydroprotoberberines on both the polar and nonpolar columns. Simultaneous resolution of mixtures of aporphines and tetrahydroprotoberberines was readily achieved on the OV-1 column. An SE-30 column, used for combined GC-MS analysis, gave a similar resolution of these alkaloids. The mass spectra observed for the silylated 1,2,9,10-substituted aporphines were similar to those of underivatized aporphines, while the mass spectra of the silylated 1,2,10,11-substituted aporphines differed markedly from the spectra of the underivatized alkaloids. Although the mass spectra of the silylated derivatives of the 2,3,9,10- and 2,3,10,11-substituted tetrahydroprotoberberines were identical, these isomeric derivatives were separated by gas chromatography.     

DETECTION OF NEW PIGMENTS FROM EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY, LIQUID CHROMATOGRAPHY–MASS SPECTROMETRY, VISIBLE SPECTROSCOPY, AND FAST ATOM BOMBARDMENT MASS SPECTROMETRY

Pigment extracts from Emiliania huxleyi (Lohm.) Hay et Mohler (strains CCMP 370, CCMP 373, and NIOZ CH 24) were analyzed using high-performance liquid chromatography (HPLC) on highly efficient monomeric and polymeric octadecylsilica columns using either ammonium acetate or pyridine containing mobile phases. Both systems showed chromatographic profiles with peaks corresponding to pigments of uncertain structure: those of the polar and nonpolar chlorophyll c forms and one peak whose on-line diode array spectrum resembled that of the fucoxanthin acyloxy derivatives. Liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry gave a molecular mass of 786 units for the unknown carotenoid. The pigments corresponding to each of these fractions were isolated and their visible spectra recorded in various solvents. Samples of the isolated pigments were subjected to analysis by fast atom bombardment mass spectrometry that confirmed a molecular mass of 786 for the unknown carotenoid and gave a mass of 654 units for the polar chlorophyll c ₃, compatible with the monovinylic structure previously suggested. The detection of these new pigments calls for attention on the use of correct methodologies when HPLC pigment signatures are used to study the taxonomic composition of natural phytoplankton populations.     

Use of liquid hydrocarbon and amide transfer data to estimate contributions to thermodynamic functions of protein folding from the removal of nonpolar and polar surface from water.

This extension of the liquid hydrocarbon model seeks to quantify the thermodynamic contributions to protein stability from the removal of nonpolar and polar surface from water. Thermodynamic data for the transfer of hydrocarbons and organic amides from water to the pure liquid phase are analyzed to obtain contributions to the thermodynamics of folding from the reduction in water-accessible surface area. Although the removal of nonpolar surface makes the dominant contribution to the standard heat capacity change of folding (delta C0fold), here we show that inclusion of the contribution from removal of polar surface allows a quantitative prediction of delta C0fold within the uncertainty of the calorimetrically determined value. Moreover, analysis of the contribution of polar surface area to the enthalpy of transfer of liquid amides provides a means of estimating the contributions from changes in nonpolar and polar surface area as well as other factors to the enthalpy of folding (delta H0fold). In addition to estimates of delta H0fold, this extension of the liquid hydrocarbon model provides a thermodynamic explanation for the observation [Privalov, P. L., & Khechinashvili, N. N. (1974) J. Mol. Biol. 86, 665-684] that the specific enthalpy of folding (cal g-1) of a number of globular proteins converges to a common value at approximately 383 K. Because amounts of nonpolar and polar surface area buried by these proteins upon folding are found to be linear functions of molar mass, estimates of both delta C0fold and delta H0fold may be obtained given only the molar mass of the protein of interest.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromatographic behavior of oxygenated derivatives of cholesterol

Oxygenated derivatives of cholesterol have important functions in many biochemical processes. These oxysterols are difficult to study because of their low physiological concentrations, the facile formation of cholesterol autoxidation artifacts, and lack of information on their chromatographic behavior. Focusing on metabolites and autoxidation products of cholesterol, we have documented the chromatographic mobilities of 35 oxysterols under a variety of conditions: eight solvent systems for thin-layer chromatography on silica gel, several mobile phases for reversed-phase high-performance liquid chromatography (HPLC), and two types of stationary phase for capillary gas chromatography (GC) using trimethylsilyl derivatives. Notable differences in selectivity could be obtained by modifying the stationary or mobile phases. Separations of oxysterol pairs isomeric at side-chain carbons or C-7 were achieved on normal-phase, reversed-phase, chiral, or silver-ion HPLC columns. Chromatographic behavior is also described for side-chain hexadeuterated and heptafluorinated oxysterols, which are useful as standards in isotope dilution analyses and autoxidation studies, respectively. The overall results are relevant to many problems of oxysterol analysis, including the initial separation of oxysterols from cholesterol, determination of highly polar and nonpolar oxysterols, separation of isomeric pairs, selection of derivatization conditions for GC analysis, and quantitation of the extent of cholesterol autoxidation.     

Movement of methylphenazyl free radicals in polar and nonpolar liquids.

A protonated, charged free radical of methylphenazine methosulfate (PMS) was generated at carbon electrodes in a buffered aqueous medium. This radical diffused from the aqueous phase into nonpolar organic solvents, where it was stable for extended periods. The electron spin resonance (ESR) spectrum of the free radical species in the nonpolar solvent was significantly different from that of the aqueous species. This difference was attributed to the loss of electric charge through deprotonation at the solution interface, followed by solvation of the uncharged species in the organic phase. ESR spectra are presented for PMS free radicals in polar and nonpolar liquid phases, along with electrochemical results and conclusions regarding the mechanisms of movement and toxicity of phenazyl free radicals in biological systems.     

The Lipid Layer: The Outer Surface of the Ocular Surface Tear Film

The outer layer of the tear film—the lipid layer—has numerous functions. It is a composite monolayer composed of a polar phase with surfactant properties and a nonpolar phase. In order to achieve an effective lipid layer, the nonpolar phase, which retards water vapor transmission, is dependent on a properly structured polar phase. Additionally, this composite lipid layer must maintain its integrity during a blink. The phases of the lipid layer depend on both lipid type as well as fatty acid and alcohol composition for functionality. Surprisingly, the importance of the composition of the aqueous layer of the tear film in proper structuring of the lipid layer has not been recognized. Finally, lipid layer abnormalities and their relationship to ocular disease are beginning to be clarified.     

Development of Ionic Liquid‐Water‐Based Thermomorphic Solvent (TMS)‐Systems for Biocatalytic Reactions

The applicability of ionic liquid‐water‐based thermomorphic solvent (TMS)‐systems with an upper critical solution temperature for homogeneous biocatalysis is investigated. Cholinium‐ and imidazolium‐based ionic liquids are used to facilitate a temperature‐dependent phase change, which can be easily fine‐tuned by adding salts or polar organic solvents. Within the TMS‐system, a high enzymatic activity and subsequent full conversion is achieved in the intermittent monophasic reaction system of the TMS‐system. Therefore, the biocatalyst can be easily recycled after separating the phases at lower temperatures.     

Enantioseparation using urea- and imide-bearing chitosan phenylcarbamate derivatives as chiral stationary phases for high-performance liquid chromatography

Completely deacetylated chitosan was prepared by the treatment of commercial chitosan with 50% aqueous NaOH, and then derivatized into several new chitosan phenylcarbamate derivatives having a urea and an imide moiety at the 2-position of the glucosamine ring by the reaction with isocyanate and phthalic anhydride/isocyanate, respectively. The chitosan derivatives were coated on macroporous silica gel and evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography. The chiral recognition ability of the chitosan derivative was improved using the completely deacetylated chitosan. Among the novel chitosan derivatives, the 3,5-dimethyl-, 3,5-dichloro-, and 3,4-dichlorophenylcarbamate derivatives were found to possess relatively high chiral resolution abilities. The CSPs based on the chitosan phenylcarbamate-urea and -imide derivatives were stable in the presence of chloroform and ethyl acetate as a component of the eluents, and some racemates were better resolved by such eluents. The dichlorophenylcarbamate-imide derivatives showed a high chiral recognition for metal acetylacetonate complexes. The enantiomerization of Al(acac)3 was performed on the chitosan 3,5-dichlorophenylcarbamate-imide derivative CSP and the resulting chromatogram showed a 26% (+)-isomer enrichment.     

Separation of mono-, di-, and trihydroxy stereoisomers of bile acids by capillary gas-liquid chromatography

Capillary gas-liquid chromatographic separation was studied for the complete set of the 26 theoretically possible isomers of mono-, di-, and trihydroxylated 5 beta-cholanic acids, which differ from one another in the number, position, and configuration of hydroxyl groups at C-3, C-7, and/or C-12 in the nucleus, as well as for some of their related acids. The bile acid samples were chromatographed as their methyl ester-trimethylsilyl (TMSi) ether derivatives and analyzed on three capillary columns coated with nonpolar OV-1, slightly polar OV-17, and polar SP-2340 as liquid phases. The retention times on capillary gas-liquid chromatography (GLC) responded dramatically to the minor structural differences, and almost complete separation of the positional and stereochemical isomers was achieved by the combined use of SP-2340 and OV-17 (or OV-1) capillary columns.     

Lipids from the guinea pig Harderian gland: use of picolinyl and other pyridine-containing derivatives to investigate the structures of novel branched-chain fatty acids and glycerol ethers

The lipid extracted from guinea pig Harderian glands was hydrolysed and the constituents were examined as trimethylsilyl (TMS), (2H9)TMS, methyl ester/TMS, acetonide/TMS, nicotinate/TMS, picolinyl/TMS and nicotinylidene/TMS derivatives by capillary gas-liquid chromatography and gas chromatography/mass spectrometry. Over 70 compounds amounting to over 93% of the extract were identified. These consisted of 1-O-alkyl glycerols (glycerol ethers) with alkyl chains containing from 17 to 21 carbon atoms and fatty acids ranging from 14 to 26 carbon atoms. The alkyl chains in the glycerol ethers were straight, mono- and dimethyl-branched with the major site of branching being at C-14. All straight-chain acids from C14 to C26 were present, with the most abundant being n-24:0. Again mono- and dimethyl branched structures comprised the bulk of the remaining acids. Methyl groups tended to be towards the middle of the chain rather than in the more usual omega-1 (iso) and omega-2 (anteiso) positions, with C-14 again being a major site. The shorter-chain acids tended to have methyl groups closer to the acid group, with several of the short-chain compounds being substituted at C-2. Structural information on the acids was provided by the picolinyl derivatives and the sample provided an opportunity to evaluate these derivatives with branched acids other than the iso and anteiso compounds studied previously. They were found to be satisfactory for analysis of both mono- and dimethyl branched acids with the possible exception of compounds containing a methyl branch at C-4. However, in this case, structural information was provided by the methyl ester.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gas-liquid chromotography of trimethylsilyl and alkyl oxime-trimethylsilyl derivatives of some prostaglandins

TMS (trimethylsilyl), MO-TMS (methyl oxime-TMS), and EO-TMS (ethyl oxime-TMS) derivatives of several prostaglandins (A, B1, B2, E1, 8-iso-E1, E2 and 8-iso-E2) were prepared and their gas chromatographic properties examined on a moderately polar (OV-17) and a relatively non-polar (SE-30) stationary phase. Combined gas chromatography-mass spectrometry (GC-MS) using an LKB 9000 instrument was used to identify the different derivatives. Although the TMS derivatives are more easily prepared, the TMS derivatives of the PgE series are thermally somewhat unstable. Thus, MO-TMS and EO-TMS derivatives which exhibit more regular retention increments are more useful for analytical work. The EO-TMS derivatives may be useful in determining mass spectral fragmentation modes of the prostaglandin derivatives.     

Steroid profiling in the study of rat testicular steroidogenesis

Twenty authentic steroids, derivatized as O-methyl oximes (MO), trimethylsilyl (TMS) ethers or as MO-TMS ethers have been subjected to capillary gas chromatography using two different columns. Virtually all of the steroid derivatives have been resolved, one difficult pair to separate being 5,16-androstadien-3 beta-ol and 5 alpha-androst-16-en-3 beta-ol on the non-selective phase OV-1. Where syn and anti forms of MO derivatives arose, these were also resolved under the conditions utilised. This technique of 'steroid profiling' has been applied to the separation and quantification of metabolites of pregnenolone which were formed during incubations of the microsomal and cytosolic fractions from rat testes. The majority of the metabolites were found in the microsomal incubation. These compounds included some odorous 16-androstenes as well as other C21 and C19 steroids, the formation of which was consistent with the 5-ene and 4-ene pathways of testosterone biosynthesis being operative. In addition, evidence was obtained for 16 alpha-hydroxylation of C21 steroids. Very much less metabolic activity was found in the cytosolic fraction of rat testes. Metabolic pathways have been proposed which both confirm and extend earlier work. We conclude that the rat testis can only form some of the odorous, possibly pheromonal, 16-androstenes and that these are quantitatively less important than in the porcine testis.     

Inhibitors of sterol synthesis. Chromatography of acetate derivatives of oxygenated sterols

The separation of the acetate derivatives of a number of oxygenated sterols was achieved by medium pressure liquid chromatography on silica gel columns and by normal and reversed phase high performance liquid chromatography. We have explored the application of these chromatographic systems for the analysis of oxygenated sterols of plasma samples from two normal human subjects. The addition of highly purified [14C]cholesterol to plasma permitted the detection and quantitation of oxygenated sterols formed by autoxidation of cholesterol during processing of the samples. Special attempts to suppress autoxidation of cholesterol included the use of an all-glass closed system for saponification and extraction under argon followed by rapid removal of cholesterol from the polar sterols by reversed phase medium pressure liquid chromatography. Chromatographic analyses of the [3H]acetate derivatives of the polar sterols provided a sensitive approach for the detection and quantitation of the individual oxygenated sterols. Oxygenated sterols detected in plasma included cholest-5-ene-3 beta,26-diol, (24S)-cholest-5-ene-3 beta,24-diol, and cholest-5-ene-3 beta,7 alpha-diol. After correction for their formation by autoxidation of cholesterol during processing of the samples, very little or none of the following sterols were observed: cholest-5-ene-3 beta,7 beta-diol, 5 alpha,6 alpha-epoxy-cholestan-3 beta-ol, 5 beta,6 beta-epoxy-cholestan-3 beta-ol, and cholestane- 3 beta, 5 alpha,6 beta-triol, and the 25-hydroxy, 22R-hydroxy, 21-hydroxy, 20 alpha-hydroxy, and 19-hydroxy derivatives of cholesterol.     

Identification by gas chromatography and mass spectrometry of lipids from the rat Harderian gland

Lipids from rat Harderian glands were extracted with ethyl acetate, hydrolysed with base and examined by gas chromatography (GC) and gas chromatography—mass spectrometry (GC—MS) as trimethylsilyl (TMS), [²H₉]TMS, methyl ester—TMS, picolinyl, nicotinate and nicotinylidene derivatives. The latter three derivatives were used to reveal the structures of the alkyl chains of fatty acids, alcohols and glycerol ethers, respectively. Forty-eight compounds were identified, representing about 97% of the total extracted lipids as measured by GC peak areas. The major constituents were fatty acids with chain lengths from 12 to 22 carbon atoms (mainly C₁₈ and C₂₀) and fatty alcohols (C₁₆ to C₂₆) derived from wax esters. Most of these acids and alcohols were unsaturated in the ω-7 position and were accompanied by smaller amounts of the saturated and ω-5 monounsaturated analogues. Glycerol ethers were also identified for the first time in this secretion; the ether chains contained from 14 to 19 carbon atoms (mainly 16) and were straight-chain saturated, unsaturated (ω-5 and ω-7) and branched (iso). The only sterol found was cholesterol amounting to 1.24% of the total extract.     

Interactions of chiral molecules with an (r)-n-(3,5-dinitrobenzoyl) phenylglycine HPLC stationary phase

Forty different chiral molecules were studied by liquid chromatography with a Pirkle-type, (R)-N-(3,5-dinitrobenzoyl) phenylglycine (DNBPG), chiral stationary phase column. The dramatic effect of a small molecular change on chiral recognition was demonstrated using DL-amino acid derivatives. The inductive effect on chiral recognition was also studied using trifluoro-, trichloro-, dichloro-, monochloroacetyl, and acetyl derivatives of four different chiral amines. The study of the enantiomer separation of 11 different crown ethers of 2,2′-binaphthyldiyl showed that the rigidity of the chiral center can be an additional parameter in chiral recognition for the DNBPG phase but not for a β-cyclodextrin bonded chiral phase. It is apparent from this study that steric effects, inductive effects, and molecular rigidity play important roles in chiral recognition with DNBPG chiral stationary phases.     

Fermentative degradation of nonionic surfactants and polyethylene glycol by enrichment cultures and by pure cultures of homoacetogenic and propionate-forming bacteria

Linear alkyl ethoxylates (polyethylene glycol alkyl ethers) were fermented completely to methane and CO2 in enrichment cultures inoculated with anoxic sewage sludge. Long-chain fatty acids were released as intermediates. No degradation was found with polypropylene glycol and polypropylene glycol-containing surfactants. Two types of primary ethoxylate-degrading bacteria were isolated and characterized. Both degraded polyethylene glycols with molecular weights of 1,000 completely. Strain KoB35 fermented polyethylene glycol, ethoxyethanol, and lactate to acetate and propionate and was assigned to the described species Pelobacter propionicus. Strain KoB58 converted polyethylene glycol and many other substrates to acetate only and was assigned to the genus Acetobacterium. The pathways of anaerobic degradation of nonionic surfactants are discussed with respect to their limitations and the various groups of bacteria involved.